Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $53.83   12.665%   $60.6476   $60.65   $60.65   $60.60  
  Purchase #2 $169.81   4.670%   $177.7401   $177.74   $177.75   $177.70  
  Purchase #3 $183.89   13.237%   $208.2315   $208.23   $208.25   $208.20  
  Purchase #4 $30.61   5.428%   $32.2715   $32.27   $32.25   $32.30  
  Purchase #5 $98.28   8.535%   $106.6682   $106.67   $106.65   $106.70  
  Purchase #6 $28.69   7.856%   $30.9439   $30.94   $30.95   $30.90  
  Purchase #7 $152.64   5.585%   $161.1649   $161.16   $161.15   $161.20  
  7 purchase totals = $717.75       $777.6677   $777.66   $777.65   $777.60